Underwater sound channel in the northeastern East China Sea

Song, Heechun,Cho, Chomgun,Hodgkiss, William,Nam, SungHyun,Kim, Sea-Moon,Kim, Byoung-Nam Elsevier 2018 Ocean engineering Vol.147 No.-

<P><B>Abstract</B></P> <P>In May 2015 a shallow-water acoustic variability experiment (SAVEX15) was conducted in the northeastern East China Sea. Surprisingly, an underwater sound channel that is typical for deep water was discovered in this shallow water waveguide (∼100 m deep) with the channel axis at around 40 m. For a broad-band source (0.5–2.0 kHz) deployed close to the channel axis, channel impulse responses observed by a vertical array exhibited a complex arrival structure with a large delay spread (e.g., 160 milliseconds). Most arrivals are found to be surface and bottom reflected, while a pair of high-intensity refracted arrivals are embedded in the early reflected arrivals. Broadband simulations based on a normal mode propagation model show good agreement with data.</P> <P><B>Highlights</B></P> <P> <UL> <LI> An underwater sound channel (USC) typical for deep water is found in the shallow northeastern East China Sea. </LI> <LI> Detailed observations on the environments and underwater acoustic data are presented. </LI> <LI> A complex structure of sound arrivals observed under the USC is separated into refracted and surface/bottom reflected ones with a broad-band simulation. </LI> </UL> </P>

Null-broadening in a waveguide

Kim, J. S.,Hodgkiss, W. S.,Kuperman, W. A.,Song, H. C. 韓國海洋大學校 附設 海洋科學技術硏究所 2002 硏究論文集 Vol.11 No.1

Null-broadening, introduced in plane wave beamforming, is extended to an ocean waveguide in the context of matched field processing. The method is based on the minimum variance processor with white noise constraint and the distribution of fictitious sources using the theory of waveguide invariants. The proposed method is demonstrated in simulation as well as with data collected during the SWellEx-96 experiment. As another application, it is shown that the width of a null can be controlled in an adaptive time reversal mirror with a source-receive array. ⓒ 2002 Acoustical Society of America. [DOI: 10.1121/1.1488139] PACS numbers : 43.60.GK, 43.30.Wi, 43.20.Fn[SAC]

High-rate multiuser communications in shallow water.

Song, H C,Kim, J S,Hodgkiss, W S,Kuperman, W A,Stevenson, M American Institute of Physics for the Acoustical S 2010 Journal of the Acoustical Society of America Vol.128 No.5

<P>Passive multiuser communications in shallow water previously was demonstrated in the 3-4 kHz band using a time reversal approach. This paper extends those experimental results in three respects. First, a larger bandwidth at higher frequency (11-19 kHz) is employed allowing for the use of various symbol rates (or bandwidths). Second, two different shaping pulses are examined: a raised cosine filter and LFM (linear frequency modulation) chirp. Third, the adaptive time reversal approach with spatial nulling is applied to suppress the crosstalk among users. It is shown that the use of a larger bandwidth is beneficial along with the time reversal receiver which can handle significant intersymbol interference with minimal computational complexity. In addition, adding each user degrades the performance by about 4 dB for the benefit of linear increase in data rate. It is demonstrated that an aggregate data rate of 60 kbits/s can be achieved with a 7.5 kHz bandwidth (a spectral efficiency of 8 bits/s?z) by three users distributed over 4.2-m depth at a 2.2 km range in shallow water using 16-QAM (quadrature amplitude modulation).</P>

Long-range multi-carrier acoustic communications in shallow water based on iterative sparse channel estimation.

Kang, Taehyuk,Song, H C,Hodgkiss, W S,Soo Kim, Jea American Institute of Physics for the Acoustical S 2010 Journal of the Acoustical Society of America Vol.128 No.6

<P>Long-range orthogonal frequency division multiplexing (OFDM) acoustic communications is demonstrated using data from the Kauai Acomms MURI 2008 (KAM08) experiment carried out in about 106 m deep shallow water west of Kauai, HI, in June 2008. The source bandwidth was 8 kHz (12-20 kHz), and the data were received by a 16-element vertical array at a distance of 8 km. Iterative sparse channel estimation is applied in conjunction with low-density parity-check decoding. In addition, the impact of diversity combining in a highly inhomogeneous underwater environment is investigated. Error-free transmission using 16-quadtrative amplitude modulation is achieved at a data rate of 10 kb/s.</P>

시변동이 있는 근거리 음향신호의 시간영역 지음향학적 역산

Park, Cheolsoo,Seong, Woojae,Gerstoft, Peter,Hodgkiss, William S. 한국음향학회 2013 韓國音響學會誌 Vol.32 No.4

2006년 여름 New Jersey 대륙붕 근해에서 일련의 해상실험(Shallow Water 2006, SW06)이 수행되었다. 이 때 수직선배열에서 계측된 근거리 chirp 신호(1100~2900 Hz)에서 직접도달파와 해수면 반사파의 강한 시변동이 관찰되었다. 본 논문은 시변동성이 있는 근거리 음향신호의 지음향학적 역산기법과 실험 데이터에 대한 역산결과를 제시한다. 불규칙한 해수면 반사파가 역산에 미치는 영향을 최소화하기 위해 수직선배열에서 음원의 위치로 직접도달 경로와 해저면 반사경로를 통해 역전파된 신호의 에너지로써 목적함수를 정의하였다. 또한 VFSR(Very Fast Simulated Reannealing) 최적화기법을 활용한 다단계 역산기법을 실험데이터에 적용하였다. 역산 결과 음원은 주기적인 수직운동을 한 것으로 파악되었고 그 주기는 수면파의 주기와 일치하였다. 해저면의 음속은 1645 m/s로 추정되었고 이는 동일 해역의 다른 연구결과와 유사한 것으로 파악되었다. A set of experiments (Shallow Water 2006, SW06) was carried out in shallow water near the New Jersey shelf break in summer 2006. Significant fluctuations in direct and surface reflected arrivals were observed from the chirp data (1100~2900 Hz) measured on a vertical line array. This paper presents a geoacoustic inverssion technique for short-range acoustic data with fluctuating arrivals and inversion results of experimental data. In order to reduce effects of random sea surface on the inversion, the acoustic energy back-propagated from the array to the source through direct and bottom-reflected paths is defined as the objective function. A multi-step inversion scheme is applied to the data using VFSR (Very Fast Simulated Reannealing) optimization technique. The inversion results show a source depth oscillation period equal to the measured ocean surface wave period. The inverted bottom sound speed is 1645 m/s and is similar to that estimated by other work at the same site.

Fluctuating arrivals of short-range acoustic data.

Park, Cheolsoo,Seong, Woojae,Gerstoft, Peter,Hodgkiss, William S American Institute of Physics for the Acoustical S 2011 JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA - Vol.129 No.1

<P>Geoacoustic inversion using fluctuating signal observations can be challenging. The origin of these fluctuations needs to be understood so the signals can be used appropriately. A set of experiments [Tang et al., Oceanogr. 20(4), 156-167 (2007)] was carried out in shallow water near the New Jersey shelf break in summer 2006. Significant fluctuations in the direct path and surface-reflected arrivals of short-range chirp transmissions (1.1-2.9 kHz) were observed on a vertical line array. This paper explains the origin of these signal fluctuations through analysis of the arrival amplitudes. It is shown that the strong thermocline combined with an oscillating source motion due to ocean surface waves results in the signal fluctuations.</P>

Distribution of Alexandrium tamarense in Drake Passage and the Threat of Harmful Algal Blooms in the Antarctic Ocean

King-Chung Ho,강성호,Ironside H. Y. Lam,I. John Hodgkiss 한국해양과학기술원 2003 Ocean and Polar Research Vol.25 No.3s

Label-Free, Electrochemical Quantitation of Potassium Ions from Femtomolar Levels.

Zhu, Bicheng,Booth, Marsilea A,Woo, Han Young,Hodgkiss, Justin M,Travas-Sejdic, Jadranka Wiley-VCH 2015 Chemistry - An Asian Journal Vol.10 No.10

<P>In this communication, a label-free and sensitive electrochemical method to detect potassium ions is proposed. The conducting polymer polypyrrole was used as both an anchor for the probe and a transducer of the detection event. A K(+) -specific G-rich aptamer was applied as a recognition element, which folded into the G-quadruplex structure in the presence of K(+) , and this resulted in an increase in the electrode impedance. The combination of the K(+) -selective aptamer and the porous conducting polymer as a signal transducer afforded a successful sensor platform. The sensor responded approximately logarithmically over a wide dynamic range of K(+) concentrations from 20?fm to 1?mm, with a very low detection limit of 14.7?fm and excellent discrimination against other ions. Additionally, electrochemical impedance spectroscopy was used to study the kinetics of K(+) binding at the conducting polymer-immobilized aptamer surface, which indicated strong binding between the two. This work demonstrates a powerful approach for the sensitive, selective, and direct electrochemical detection of metal ions based on the switching conformation of G-rich aptamers attached to a porous conducting polymer surface. This assay scheme can be expanded to the detection of a wide range of targets by modifying the aptamer structure as a recognizing moiety.</P>

Thermochromism, Franck–Condon Analysis and Interfacial Dynamics of a Donor–Acceptor Copolymer with a Low Band Gap

Reish, Matthew E.,Huff, Gregory S.,Lee, Wonho,Uddin, Mohammad Afsar,Barker, Alex J.,Gallaher, Joseph K.,Hodgkiss, Justin M.,Woo, Han Young,Gordon, Keith C. American Chemical Society 2015 Chemistry of materials Vol.27 No.8

<P>The electronic properties of the donor–acceptor (DA) polymer poly{5,6-bis(octyloxy)-4-(thiophen-2-yl)benzo[<I>c</I>]-1,2,5-thiadiazole} (PTBT) have been investigated using spectroscopic and computational techniques. Electronic absorption and emission spectra reveal the presence of an ordered and a disordered phase in solution. Franck–Condon modeling of the ordered phase yields Huang–Rhys factors of 0.55 (20 °C) and 0.51 (−180 °C), indicating little structural distortion between ground and excited state. DFT calculations with resonance Raman spectroscopy are consistent with a lowest energy excited state that is electronically delocalized and has little charge-transfer character, unexpected for a copolymer with a low bandgap (∼1.8 eV). Transient absorption spectroscopy of PTBT:fullerene blends reveals near-unity internal charge-transfer yields in both ordered and disordered film morphologies. In the disordered blend, charge transfer is complete within the laser pulse (100 fs), whereas the ordered blend also features a slower phase due to exciton diffusion in the phase separated morphology. In the ordered blend, the spectra and dynamics of charge transfer reveal that excitons and charges promptly occupy delocalized states on extended polymer chains. The pervasive use of donor–acceptor structures in polymer devices makes understanding the interplay of morphology and electronic structure of these polymers essential and here a spectroscopic and computational investigation gives an extensive picture of the electronic properties and their effect on charge dynamics in a DA polymer.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/cmatex/2015/cmatex.2015.27.issue-8/cm504655f/production/images/medium/cm-2014-04655f_0009.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/cm504655f'>ACS Electronic Supporting Info</A></P>

Spectroscopically tracking charge separation in polymer : fullerene blends with a three-phase morphology

Gallaher, Joseph K.,Prasad, Shyamal K. K.,Uddin, Mohammad A.,Kim, Taehyo,Kim, Jin Young,Woo, Han Young,Hodgkiss, Justin M. The Royal Society of Chemistry 2015 Energy & environmental science Vol.8 No.9

<P>The coexistence of intermixed amorphous polymer : fullerene phases alongside pure semicrystalline polymer and fullerene phases provides a plausible explanation for effective charge separation in organic photovoltaic blends by providing a cascaded energy landscape. We sought to test this proposal by spectroscopically tracking charge dynamics in 3-phase blends compared with binary counterparts and linking these dynamics to free charge yields. Our study applies broadband transient absorption spectroscopy to a series of closely related alternating thiophene-benzothiadiazole copolymers in which the tuned curvature of the polymer backbone controls the nature and degree of polymer-fullerene intermixing. Free charge generation is most efficient in the 3-phase morphology that features intimately mixed polymer : PCBM regions amongst neat polymer and PCBM phases. TA spectral dynamics and polarization anisotropy measurements reveal the sub-nanosecond migration of holes from intermixed to pure polymer regions of such blends. In contrast, 2-phase blends lack the spectral dynamics of this charge migration process and suffer from severe geminate recombination losses. These results provide valuable spectroscopic evidence for an efficient charge separation pathway that relies on the 3-phase morphology.</P>